IP Networks
IP networks cover routing, service edge, and packet forwarding in Nokia 7750 SR and FP5-based platforms. The exam tests routing logic, segment routing, EVPN services, BNG subscriber handling, QoS, and how control-plane decisions map to data-plane behavior.
Routing and service edge
IP forwarding uses longest-prefix match. BGP selects routes using attributes such as weight, local preference, AS path length, origin, MED, and router ID; the exact order depends on implementation, so know the platform's rules. Segment routing uses SR-MPLS or SRv6 to steer traffic with source-encoded paths; TI-LFA provides fast repair. A BNG terminates subscriber sessions, applies per-subscriber QoS and accounting, and enforces policy. QoS requires consistent DSCP marking, classification, queuing, and scheduling across domains.
Rules to apply
- Longest-prefix match wins before any BGP attribute comparison.
- A control-plane route preference does not automatically define data-plane QoS.
- TI-LFA repairs a failed path using a precomputed backup; it is not a full re-convergence.
- Subscriber QoS at the BNG must handle untrusted markings from customer equipment.
- Segment routing requires consistent SRGB and label handling across the domain.
Worked example
A customer CPE sends packets marked EF, but the SLA only guarantees EF after BNG authentication. The BNG classifies the subscriber, remarks untrusted traffic, maps the service to a forwarding class, and schedules it with a guaranteed share. The reasoning: trust boundaries matter; customer marking alone cannot create priority. If the subscriber is authenticated and authorized for EF, the marking can be preserved under policy.
Traps that cost marks
Assuming BGP attributes override longest-prefix match; trusting CPE DSCP without a trust boundary; confusing TI-LFA with full BGP re-convergence; and ignoring per-subscriber QoS at the BNG.